Hi Liz 

Thanks for posting in the Community! Are you referring to the arrows at the end of lines? To learn more about how to use lines please check out this Help Center article. Here you'll find directions on how to add modify and customize lines. 

Currently customizable arrows at the end of lines aren't supported in Lucidchart; the full list of options can be seen here in the Endpoint dropdown menus in the toolbar at the top of the editor. 

However I certainly understand how custom endpoints could be useful! If you'd like to see this implemented in the future would you mind adding your idea and use case details to this feature request form? Ideas submitted here help our development team prioritize improvements to Lucidchart. Thanks for your request and apologies for any inconvenience. Please let me know if you have additional questions!